The problem of parasite biodiversity is considered from 2 aspects: (1) estimation of proper parasite diversity; (2) estimation of parasite role in diversity changes resulting all free-living organisms on the Earth, that is more essential. The paper covers problems of parasite diversity and parasitic systems being formed (parasite communities) which, apart from parasites, are known to include numerous free-living organisms acting as parasite partners in parasitic chains, i.e. different (final, intermediate, additional, etc.) hosts. Parasites are closely associated with the latter by complex parasite-host interrelations and significantly influence them at all levels of organization. Examples are given that illustrating role of parasitic organisms in the problem of biodiversity.